Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.     

Impact of tailings dam failure on spatial features of copper contamination (Mazraeh mine area,Iran)

Mining activities pose a potential risk of metal contamination around mining sites. On May 6, 2010, a tailings dam failure of the Mazraeh copper mine near Ahar in East Azerbaijan province, Iran, released vast amounts of mine wastes. To better understand the magnitude of copper contamination in the waste-affected soils, it is important to assess the spatial distribution of soil copper content at unsampled points. A total of 30 soil samples and their surficial sediments together with the 6 uncontaminated control samples (0–10 and 10–30 cm) were collected along the stream flow that joined Ahar-Chai River. Some of soil properties as well as total copper concentration were determined in all samples. The mean value of the latter in the surface contaminated soils was found to be approximately two times more than controls. Furthermore, the mean concentration of copper in the surface loaded material was 10 times more than the soils. High copper concentrations were observed in surficial sediments of the soils near the broken tailings dam. The Inverse Distance Weighting (IDW) method was employed in data analysis. The spherical and Gaussian semivariogram models were properly fitted to the data of copper contents in soils and surficial sediments.     

Sequential extraction and leaching characteristics of heavy metals in abandoned tungsten mine tailings sediments

The chemical speciation of potentially toxic elements (As, Cd, Cu, Pb, and Zn) in the contaminated soils and sulfides-rich tailings sediments of an abandoned tungsten mine in Korea was evaluated by conducting modified BCR sequential extraction tests. Kinetic and static batch leaching tests were also conducted to evaluate the potential release of As and other heavy metals by acidic rain water and the leaching behaviors of these heavy metals. The major sources of the elements were As-, Zn- and Pb-bearing sulfides, Pb carbonates (i.e., cerussite), and Pb sulfates (i.e., anglesite). The biggest pollutant fraction in these soil and tailing samples consists of metals bound to the oxidizable host phase, which can be released into the environment if conditions become oxidative, and/or to residual fractions. No significant difference in total element concentrations was observed between the tailings sediments and contaminated soils. For both sample types, almost no changes occurred in the mobility of As and the other heavy metals at 7 days, but the mobility increased afterwards until the end of the tests at 30 days, regardless of the initial pH. However, the mobility was approximately 5–10 times higher at initial pH 1.0 than at initial pHs of 3.0 and 5.0. The leached amounts of all the heavy metal contents were higher from tailings sediments than from contaminated soils at pH > 3.0, but were lower at pH < 3.0 except for As. Results of this study suggest that further dissolution of heavy metals from soil and tailing samples may occur during extended rainfall, resulting in a serious threat to surface and groundwater in the mine area.     

Effects of pH on arsenic mineralogy and stability in Poldice Valley,Cornwall, United Kingdom

Many abandoned mine sites in Cornwall, UK, are characterised by elevated concentrations of arsenic (As), which can cause contamination of surrounding soil and water resources. These sites have important historical value that requires access to be maintained, despite exposure of humans to toxins that may lead to health issues including hyperpigmentation keratosis (including skin cancers) and liver fibrosis. The abandoned mine tailings at Wheal Maid has been assessed for As-bearing mineralogy and stability taking into account the public footpaths made by the local council to areas of potential contamination.To assess the potential risk associated with these mine sites, the As concentration in waters along the tailings dam and Carnon River have been measured and range up to 3.6 ppm, which is 2 orders of magnitude above the WHO guideline value of 0.01 ppm for drinking water. Samples of water, rocks and soils from the mine tailings ponds and the Carnon River were analysed using Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) to determine the concentration of individual elements in each sample followed by mineral identification using X-Ray Diffraction (XRD). Mineralogical evaluation indicated that the majority of mine tailings consist of clay-rich rocks, with few associated As-bearing minerals. Scorodite (FeAsO₄·2H₂O) is observed in the mine tailings pond and appears critical to the As distribution and storage in this surface environment. Using the analysed water chemistry, a modified version of PHREEQC is used to calculate the saturation index of scorodite as a function of pH conditions. The strong variation of the solubility of this mineral with pH and oxidation state highlights potential risks for using scorodite for As fixation and storage.     

Temporal variation in the arsenic and metal accumulation in the maritime pine tree grown on contaminated soils

The uptake of arsenic and other metals (iron, manganese, copper, zinc, lead, nickel and tungsten) by Pinus pinaster Aiton (the maritime pine tree) growing in soils and tailings around an abandoned mine (northern Portugal) was investigated. Aerial parts of Pinus pinaster trees were sampled from three substrate areas: a background area, in mine contaminated soils and in tailings. Vegetation material was separated into needles and stems and subdivided into tissues of different maturities (1-, 2-, 3- and 4-years-old). The sampling of the substrate in each area was also undertaken. In general, vegetation concentrations were strongly related to substrate concentrations. The results show that the contents of several elements depend as much on the plant organ as on the age of the tissue. For the researched elements, this species shows a great variability in behavior depending on the age of the organ. The data indicate that the older needles constitute the best samples for use in a conjunct biogeochemical analysis of these elements.     

华南地区含硫化物金属矿山生态环境中的重金属元素地球化学迁移模型——重点对粤北大宝山铁铜多金属矿山的观察

粤北大宝山是华南金属成矿带的大型铁铜、铅、锌、钼等多金属综合性矿床,富含硫化物,位于北江支流横石河的上游分水岭,流域封闭性很好。矿山开发引起横石河下游的上坝村成为远近闻名的"癌症"村,部分村民出现"痛痛病"疑似症状。由于其特殊的地理位置和对下游引发的严重污染,该矿山成为研究湿热地区含硫化物金属矿山重金属元素生态-环境地球化学迁移的理想场所。以Zn为例,该矿山重金属元素从矿体中向生物体迁移过程经过尾砂/水反应界面、水/沉积物反应界面、土壤/间隙水溶液界面和土壤/植物界面4个重要的反应界面。其中,尾砂/水反应界面控制重金属从源头尾砂中的释放;水/沉积物反应界面控制重金属在水体中与河流沉积物的沉淀与释放的平衡;土壤/间隙水溶液界面控制土壤生物有效性;土壤/植物界面控制生物对重金属的吸收与利用。4个界面的介质间相互作用较好地刻画大宝山矿山因为开采,重金属元素从内生环境中曝露出来,然后在表生环境中释放、迁移、转化、归宿的迁移模式。上述认识对矿山重金属污染治理具有重要的指导意义。通过改变重金属迁移反应界面的条件,可以阻断矿山元素的迁移,达到污染治理的目的。     

Environmental impact and geochemistry of old tailing pile from the Sanggok mine creek, Republic of Korea

This study evaluates the pollution load on a creek based on the physicochemical and mineralogical properties of old tailings. The Sanggok mine is one of the largest lead–zinc producers in the Hwanggangri mining district, Republic of Korea. The vertical profile of the old tailings in the mine area can be divided into three units based on color change, and mineralogical and textural variations, as well as physical and chemical properties. Unit I (surface accumulation and oxidized heterogeneous tailing soil) has lower pH and higher Eh than unit II (originally unoxidized dumped tailing soil) and unit III (pebble-bearing bottom soil). The conductivity data indicates that unit I and II have very high values compared to unit III and basement. The mine area consists mainly of carbonate rocks; however, mineral constituents of tailing soil and sediments near the mine were mainly composed of quartz, mica, feldspar, amphibole, calcite, dolomite, magnesite, and clay minerals. Units I and II are characterized by high abundances of siderite, locally pyrite, and dolomite. Precipitates in the mining drainage mainly included: smectite, illite, berthierine, quartz, siderite, hexahydrite, and Ca-ferrate. Among the separated metallic minerals, tailing soils and sediments of highly concentrated toxic metals are found: some pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, malachite, goethite, various hydroxide, and uncertain secondary minerals. Units I and II are characterized by relatively high concentrations of Ca, Fe, Mn and low contents of Al, Mg, K, Na, Ti, rare earth elements (REEs) that correlated with the proportion of secondary minerals. Potentially toxic elements such as Ag, As, Cd, Cu, Pb, Sb, and Zn are highly enriched in the upper two units. This metal concentration can be influenced by changes in the depth because of oxic and suboxic zonal distribution. The removal zone (unit I) has probably migrated below the elevation of the maximum enrichment layer due to deepening of the oxic/suboxic boundary. In most of the materials, the enrichment index is higher than 3.62. The highest value of 42.55 is found in the oxidation surface soils of the tailing pile. An average enrichment index of the profiles and precipitates are 27.62 and 22.62, respectively. Rocky basement soils have an average enrichment index of 6.63, which is influenced by overlying the tailing pile. The water quality and habitat of the Sanggok creek are severely polluted. Polluted surface water may also negatively impact the agricultural soil and groundwater.     

湘中HJC铀矿区黑色页岩土壤重金属污染地球化学分析

本文以湘中HJC铀矿区黑色页岩土壤为研究对象,对黑色页岩土壤重金属污染进行了地球化学分析。通过测制A、B、C、D等土壤剖面并系统取样,借助ICPMS等分析技术,对土壤、成土母岩、玉米等进行了系统的主量元素、重金属和其他微量元素（稀土元素）分析。结果表明,矿区黑色页岩土壤具富Al2O3、Fe2O3,而贫CaO、Na2O的化学组成特征,其化学风化指数CIA值在79~84之间。土壤因继承成土母岩的元素富集特征而富集V、Cr、Co、Ni、Cu、Zn、Mo、Cd、Sn、Sb、Tl、Pb、Th、U等多种重金属,其中Mo、Cd、Sb、U的富集最强。土壤重金属综合富集指数（EI值）在3~9之间,各剖面EI值大小顺序是：D>A>B>C, 以D剖面土壤重金属综合富集最强。土壤重金属污染富集因子（F）评价结果显示：矿区土壤普遍存在Cd、Mo、Sn、Sb、U等重金属污染,其中Mo、Cd、Sb等的污染最强,达显著（3级,2 < F < 20）污染程度以上。重金属污染效应既表现为Sc、Cd、Sn、Sb、U、Tl、Pb等生物毒性重金属在玉米中的富集,又表现为Mo、Co、Ni、Cu、Zn等生物有用金属在玉米中的明显亏损。黑色页岩即为土壤重金属污染的污染源。土壤重金属污染与重金属在成土母岩和土壤中的富集程度(Ks、EI、F)、重金属的活动性（Change%）等多种因素有关。重金属污染主影响因子的Pearson相关系数分析显示：Cd对土壤构成持久性污染,Mo、Sn、Sb、U等的污染程度可随土壤风化的进行因淋失而趋于降低,而Zn、Mn、Ba、Co、Ni、Th等目前未达到污染水平的重金属则可因次生富集而在未来引发污染。     

粤北大宝山矿酸性排水中铅元素环境地球化学

粤北大宝山铁多金属矿床的开发给环境带来了严重的危害。采选冶产生的酸性排水及固体废弃物堆积的淋滤酸水,携带浸滤出的大量重金属离子流入下游河道,严重影响矿区及酸水流域的生态环境。结果表明,河流水中高Pb含量直接源于尾砂,并受水体pH值的显著影响。河流底泥能够大量聚集水体中的Pb,在水体pH值降低时,相对稳定存在的Pb会被再次从河流底泥中释放出来,形成河流二次污染。土壤中Pb含量受土壤pH值和土壤粒度的影响,食用蔬菜中Pb的高含量由土壤Pb高含量决定,并受土壤pH值的影响,通过改善农业灌溉水质,提高土壤pH值,可以降低蔬菜重金属Pb含量。     

安徽铜陵林冲尾矿库重金属元素分布与迁移及其环境影响

通过对铜陵凤凰山矿林冲尾矿库中重金属元素的空间分布特征及相关土壤、水系沉积物和植物中重金属元素含量变化的研究，初步了解尾矿重金属元素的空间变化和迁移规律，分析了其对周围环境的影响及潜在危害性，并指出了尾矿库土地综合开发利用的方向。     

Arsenic mobilization from mine tailings in the presence of a biosurfactant

Batch experiments were conducted to investigate As mobilization from mine tailings in the presence of a biosurfactant (JBR425, mixed rhamnolipids) and to evaluate the feasibility of using biosurfactant in remediating As contaminated mine tailings/soils. Introduction of the biosurfactant increased As mobilization greatly. When the mass ratio was 10 mg biosurfactant/g mine tailings at pH 11, As mobilization by the biosurfactant was greatest after 24 h, with a corresponding concentration ratio (the ratio of As mobilization by the biosurfactant to that by distilled water at same adjusted pH, wt/wt) of 21.6. Selective sequential extraction indicated that As was easily mobilized from the weakly bound and relatively more mobile fractions by washing with the biosurfactant. A mobilization isotherm was developed to predict As mobilization from the mine tailings in the presence of biosurfactant. It was shown that biosurfactant sorption to the mine tailings is essential for As mobilization. Arsenic mobilization was found to be positively correlated with the mobilization of Fe and other metals (i.e., Cu, Pb and Zn), which might further enhance As mobilization by helping incorporate it into soluble complexes or micelles. Capillary electrophoresis analyses indicated that As redox or methylation reactions had insignificant effect on As mobilization. Biosurfactants might be used potentially to remove bulk As from mine tailings or contaminated soils under alkaline conditions.     

粤北大宝山矿尾矿铅污染迁移及生态系统环境响应

粤北大宝山铁多金属矿床的开发给环境带来了严重的危害。采选冶产生的废液及固体废弃物堆积的淋滤酸水, 携带浸滤出的大量重金属离子随着酸水排入下游河道, 严重影响矿区及酸水流域的生态环境。将矿床-土壤（含河流底泥）-水体-生命体视为统一的生态环境系统, 从尾砂、水体、河流底泥、土壤以及食用蔬菜等方面探讨整个环境系统对重金属Pb的环境响应。结果表明： 河流水中高Pb含量直接源于尾砂, 并受水体pH值的显著影响; 河流底泥能够大量聚集水体中的Pb, 在高pH值时, 相对稳定存在, 在水体pH值降低时, Pb会被再次从河流底泥中释放出来, 形成河流二次污染; 土壤中Pb含量受土壤pH值和土壤粒度的影响; 食用蔬菜中Pb的高含量受土壤Pb高含量决定, 并受土壤pH值的影响, 通过改善农业灌溉水质, 提高土壤pH值, 可以降低蔬菜重金属Pb含量。     

黔西南Au-As-Hg-Tl矿化区毒害金属元素的水地球化学

研究了黔西南典型Ａｕ－Ａｓ－Ｈｇ－Ｔｌ矿化区内毒害金属元素在采矿活动和自然状态影响下的水地球化学特征及其环境效应。结果表明,已开采的Ｈｇ－Ｔｌ矿区地下水和地表水中均有很高的毒害金属元素,煤采区地下水中亦表现出类似的特征,而Ｈｇ－Ｔｌ矿区外围地下水中金属元素保持在较低的水平。Ｈｇ－Ｔｌ矿区地素水中Ａｓ和Ｔｌ的分布模式表明,其含量的变化受矿区地下水排泄和尾矿淋滤作用的控制。在尚未开采的金矿区,浅层地下     

Distribution of trace elements in soils surrounding the El Teniente porphyry copper deposit,Chile: the influence of smelter emissions and a tailings deposit

In the area surrounding the El Teniente giant porphyry copper deposit, eight soil sites were sampled at three depth levels in the summer 2004. The sites were selected for their theoretical potential of being influenced by past SO₂ emissions from the smelter and/or seepage from a now idle tailings impoundment. The soil mineralogy, grain size distribution, total organic matter contents, major element composition, cation exchange capacity, and Cu, Mo, Pb, Zn, As and SO₄ ²⁻ concentrations were determined for all samples after nitric acid extraction and separate leaches by ammonium acetate (pH 7) and sodium acetate (pH 5). For water rinses, only Cu could be determined with the analytical set-up used. Cu and SO₄ ²⁻ enrichment in topsoils was found at six sites either downwind from the smelter or within the combined influence of the smelter and the tailings impoundment. Both elements were released partially by ammonium and sodium acetate extractions. Due to the scarce background trace element concentrations of soil and rock outside the immediate mine area, assessment of trace element mobility for Mo, Zn, Pb and As was difficult. Arsenic was found to be concentrated in soil horizons with high smectite and/or organic matter contents. Mo appears to be linked to the presence of windblown tailings sediment in the soils. Mobilization of Mo, Zn, and As for the acetate extractions was minimal or below the detection limits for the AAS technique used. The presence of windblown tailings is considered to be an additional impact on the soils in the foothills of the El Teniente compound, together with the potential of acidity surges and Cu mobilization in topsoils after rainfalls. Two sites located at the western limit of the former SO₂ saturated zone with strongly zeolitized soils and underlying rock did not show any Cu or SO₄ ²⁻ enrichment in the topsoils, and remaining total trace element concentrations were below the known regional background levels.     

Assessment of Hg-contamination in soils and stream sediments in the mineral district of Nambija,Ecuadorian Amazon (example of an impacted area affected by artisanal gold mining)

The Nambija Mineral District (NMD) is located in the southeastern part of Ecuador, east of Zamora (Zamora Chinchípe's country), Ecuadorian Amazon. In this district, Au occurrences have been know since colonial and pre-colonial times, but only after the early 1980s has intensive artisanal Au mining activity been developed. Currently, the different NMD Au occurrences continue to be exploited by artisanal operations and are difficult to control in the study area. The environmental impacts due to Au mining are a consequence of the illegal situation and deficiency in controlling the techniques of ore exploitation. The Au extraction is carried out by outdoor amalgamation, so the indiscriminate use of Hg by artisanal miners, associated with careless methods of tailings disposal, has caused occupational exposure and environmental degradation. The present study evaluated the geochemical dispersion and concentrations of local contamination of metallic Hg in soils, stream sediments and mine tailings in the NMD area. This article aims to contribute to the discussion of environmental changes caused by the artisanal Au mining in the Nambija district. A total of 82 samples (32 soil, 40 stream sediment and 10 mine tailings) were analyzed. The results were compared with the Hg levels in soil and stream sediments considered not to be contaminated in the Nambija mining area and in other areas where Hg is mined in the Amazon basin. In this work, mean total Hg (T-Hg) concentrations of 1.7 μg g⁻¹ in soils and 2.7 μg g⁻¹ in stream sediments have been found. Mercury values in the mine tailing samples revealed values ranging from 89 to 1555 μg g⁻¹. The results found for Hg in the different analyzed materials pointed to contamination of the studied area by this metal, while soil erosion is responsible for an increase in stream sediment's T-Hg concentrations in the different aquatic ecosystems of the Nambija Creek and Nambija River.     

Sequential extractions on mine tailings samples after and before bioassays: implications on the speciation of metals during microbial re-colonization

Mine tailings may be remediated using metal tolerant microorganisms as they may solve the limiting conditions for healthy development of plants (i.e., low organic mater content and poor physical conditions). The aim of this study was to investigate the consequences of microbial colonization on the chemical speciation of trace metals. Surface samples from the Valenciana mine tailings (Guanajuato, Mexico) were used for long-term bioassays (BA), which consisted in the promotion of microorganisms, development on tailings material under stable laboratory conditions (humidity, temperature, and light exposure). A five-step sequential extraction method (exchangeable, carbonate/specifically adsorbed, Fe–Mn oxides, organic matter (OM)/sulfide, and residual fractions) was performed before and after BA. Extraction solutions and leachates were analyzed by inductively coupled plasma-mass spectrometry. OM content, cationic exchange capacity, and pH values were also assessed before and after BA. The results indicate that trace elements are generally present in nonresidual fractions, mainly in the Fe–Mn oxides fraction. The concentration of total Zn, As, Se, Pb, and exchangeable Cu and Pb is above the recommendable limits for soils. Despite the high bioavailability of the former elements, biofilms successfully colonized the tailing samples during the BA. Cyanobacteria and green algae, heterotrophic fungi, aerobic bacteria, and anaerobic bacteria composed the developed biofilms. Chemical controls of trace elements could be attributed to absorption onto inorganic complexes (carbonates, metal oxides), while biofilm occurrence seems to enhance complexation and immobilization of Cr, Ni, Cu, Zn, As, and Pb. The biofilm developed does not increase the bioavailable forms and the leaching of the trace elements, but significantly improves the OM contents (natural fertilization). The results suggest that biofilms are useful during the first steps of the mine tailings remediation.     

Particle-size dependence on metal(loid) distributions in mine wastes: Implications for water contamination and human exposure

The mining and processing of metal-bearing ores has resulted in contamination issues where waste materials from abandoned mines remain in piles of untreated and unconsolidated material, posing the potential for waterborne and airborne transport of toxic elements. This study presents a systematic method of particle size separation, mass distribution, and bulk chemical analysis for mine tailings and adjacent background soil samples from the Rand historic mining district, California, in order to assess particle size distribution and related trends in metal(loid) concentration as a function of particle size. Mine tailings produced through stamp milling and leaching processes were found to have both a narrower and finer particle size distribution than background samples, with significant fractions of particles available in a size range (?250 μm) that could be incidentally ingested. In both tailings and background samples, the majority of trace metal(loid)s display an inverse relationship between concentration and particle size, resulting in higher proportions of As, Cr, Cu, Pb and Zn in finer-sized fractions which are more susceptible to both water- and wind-borne transport as well as ingestion and/or inhalation. Established regulatory screening levels for such elements may, therefore, significantly underestimate potential exposure risk if relying solely on bulk sample concentrations to guide remediation decisions. Correlations in elemental concentration trends (such as between As and Fe) indicate relationships between elements that may be relevant to their chemical speciation.     

Assessment of trace metals contamination in stream sediments and soils in Abuja leather mining,southwestern Nigeria

This study is aimed at determining the level of environmental degradation as well as the concentration of trace elements in soil and stream sediments in order to evaluate the environmental impact of the mining operation. Twenty-five (25) soils and ten (10) stream sediment samples were collected from the study area. The physicochemical parameters were determined using appropriate instrumentation with the aid of a digital pH meter (Milwaukee meter) to measure the pH and electrical conductivity, total dissolved solids, moisture content and loss on ignition of the soil and stream sediment samples. The pH of the soil sample ranged from (6.10 to 7.19); Electrical conductivity ranged from (21.3 to 279.4 µS/cm), moisture content varied from (0.60% to 7.20%), and the LOI ranged from (2.03% to 18.62%). The results of the analysis showed that the concentrations of the trace elements in the soils and stream sediment samples were slightly higher than the background values. Plots of the trace elements in stream sediment samples show moderate, consistent decrease downstream except at points where there was mine water discharge into the main river. The pollution levels of heavy metals were examined in stream sediment and soil samples using different assessable indices, such as the enrichment factor, which showed significant-moderate enrichment for Cr, Th, Nb, Zn, Pb, Y and Zr and the geo-accumulation index, which showed practically moderate contamination with Cr, Ni and Sr based on regional background reference values. Geo-accumulation index and contamination index for soils and stream sediment revealed uncontaminated to moderate contamination. Likewise, elements with moderate contamination were Cr, Ni and Sr. The Pearson correlation showed that there were significant positive associations among selected metals in soil and stream sediment samples.     

Mine drainage from the weathering of sulfide minerals and magnetite

Pyrite and pyrrhotite are the principal minerals that generate acid drainage in mine wastes. Low-pH conditions derived from Fe-sulfide oxidation result in the mobilization of contaminant metals (such as Zn, Cd, Ni and Cr) and metalloids (such as As) which are of environmental concern. This paper uses data from detailed mineralogical and geochemical studies conducted at two Canadian tailings impoundments to examine the mineralogical changes that pyrite, pyrrhotite, sphalerite and magnetite undergo during and after sulfide oxidation, and the subsequent release and attenuation of associated trace elements. The stability of sphalerite in tailings impoundments generally is greater than that of pyrrhotite, but less than pyrite. Dissolved Ni and Co derived from Fe sulfides, and to a lesser extent, dissolved Zn and Cd from sphalerite, are commonly attenuated by early-formed Fe oxyhydroxides. As oxidation progresses, a recycling occurs due to continued leaching from low-pH pore waters and because the crystallinity of Fe oxyhydroxides gradually increases which decreases their sorptive capacity. Unlike many other elements, such as Cu, Pb and Cr, which form secondary minerals or remain incorporated into mature Fe oxyhydroxides, Zn and Ni become mobile. Magnetite, which is a potential source of Cr, is relatively stable except under extremely low-pH conditions. A conceptual model for the sequence of events that typically occurs in an oxidizing tailings impoundment is developed outlining the progressive oxidation of a unit of mine waste containing a mixed assemblage of pyrrhotite and pyrite.     

典型铜镍矿区周围环境介质中重金属及其化学形态分布特征

重金属污染是金属矿山开采和冶炼所引起的主要环境问题。对甘肃省典型矿业城市金昌市周围农田土壤、废渣堆表面风化物及降尘、尾矿坝尾矿砂和尾矿坝旁排污沟沉积物中Cr、Cu、Ni、Pb、Zn含量及其化学形态进行分析。结果表明:不同区域环境中重金属呈现不同程度累积,其中以Cu、Ni最为显著,含量由高到低依次为尾矿坝排污沟>尾矿坝>废渣堆>农田土壤;尾矿砂和沉积物中重金属分布以Ni含量显著高于Cu含量为特征;而农田土壤和风化物及降尘中重金属分布以Cu含量高于Ni含量为特征,前者Cu、Ni主要来源于尾矿,后者与冶炼烟尘排放有很大关系;样品中除Cr、Zn以残渣态为主外,Cu、Ni、Pb化学形态分布有较大差异,Cu以可氧化态和残渣态为主,Ni以可还原态为主,其次为弱酸提取态,Pb以可还原态为主,其次为残渣态。土壤理化性质是影响重金属化学形态分布的重要因素。